Human Digestive System

To some, digestion may seem like a simple process. However, it's actually a complex process with lots of different things happening all at once. It involves physical and chemical processes to break down food to gain the nutrients we need to survive! Digestion is just one of the processes that take place in our bodies. It takes place all along the digestive system, a series of organs including the mouth, stomach and intestines that work together to digest food. Other systems in the body include the respiratory system, nervous system, circulatory system and more! In this article, we'll focus on the digestive system, the process, and its function in humans!

Digestion is the process of breaking down larger insoluble substances into smaller soluble substances that can be absorbed into the bloodstream and used across the body. Digestion is carried out by the digestive system. Digestion is an extremely important process in our bodies. It allows us to get the important nutrients we need to grow and gain energy.

Digestion takes place all along the digestive tract (the alimentary canal). This starts with the mouth and passes all the way through to the anus, with many different organs involved the whole way through. Each organ plays its own role in helping in the digestive process.

Human Digestive System Process

The first step of the digestive process is ingestion, the process by which food enters the digestive system through the mouth. This is essential as it allows food to enter the alimentary canal.

The following overview briefly outlines the remaining steps of the digestive process.

• Digestion directly follows ingestion, starting in the mouth with the enzyme amylase in the salivary glands. Digestion is the process of breaking down large insoluble molecules into small soluble molecules. This process continues all the way from the mouth through the stomach into the intestines.
• Absorption follows digestion. It is the process of moving digested molecules from the digestive system into the bloodstream. Absorption primarily occurs in the small intestine, more specifically in the ileum.
• Assimilation follows absorption. This is the process by which absorbed molecules present in the blood then travel from the bloodstream into the cells across the body that need them. This is a vital part of the process as it allows us to make use of the foods that we have eaten.
• Egestion is the process at the very end of the digestive system. It refers to the removal of 'waste' products that have not been absorbed by the body into the bloodstream through the anus.

Human Digestive System Diagram

As we have discussed above, many organs are involved in the process of digestion. Have a look at the organs involved below and a summary of their roles in the next section.

Before looking at their roles, have a look at their location in the human body. We describe food's route through the body as the alimentary tract, digestive tract or alimentary canal.

Enzymes of the Human Digestive System

Enzymes are proteins, a type of biological molecule! Enzymes function as biological catalysts (biocatalysts). This means that, like other catalysts, enzymes speed up chemical reactions by facilitating the interactions between the reactants or substrates. Enzymes do this by lowering the activation energy of important reactions in our bodies. As catalysts, they're also not used up in the reactions they facilitate. There are enzymes in our bodies for a variety of functions, including facilitating digestion.

Fig. 2 - The lock and key theory suggests that the enzyme and substrate perfectly fit into each other

Enzyme's Role in Digestion

Many different factors affect enzyme activity. Temperature, in particular, can have a huge impact on enzyme activity. Every enzyme has an optimum temperature where its activity is highest. If we go too far above or below this temperature, the enzyme becomes denatured or inactivated and changes shape, leading to decreased enzyme activity.

Types of Digestive Systems

There are many different types of digestive systems. Different types of organisms have different digestive systems. The digestive system humans have, where we eat food using our mouth, then it passes through a long alimentary canal and then is excreted through the anus, is not the only type of digestive system! This is an example of a monogastric digestive system, where the organism only has one stomach. Other examples include the avian digestive system, found in poultry like chicken, and the ruminant digestive system found in cattle and other similar animals.

Carnivore vs Human Digestive System

What's the difference between a carnivore and human digestive systems? Well, let's start by reminding ourselves what a carnivore is.

There are a few differences between our digestive system and the digestive system of strict carnivores. However, there are more similarities than differences. The reason for this is that we, like carnivores, eat meat. As we eat the same foods, in some part, our digestive systems are similar. One area where we can find both similarities and differences is our teeth. If we look at a lion's teeth and then at our own teeth, we notice that some of our teeth have similar shapes, but others are very different. This difference is likely due to the meat that we eat. The meat we eat is often cooked softer, whereas a lion (or a similar animal) has to eat tougher, uncooked meat.

Another difference between the human digestive system and the digestive system of stricter carnivores is the length of our intestines. In humans, the digestive system contains longer intestines. This is needed to break down plant-based products in digestion.

As you can see there are many concepts to explore further related to the digestive system! Even though for us digestion might seem like just chewing and swallowing food, there are many processes that need to happen for us to be able to digest and absorb the nutrients in our food.